1. Field of the Invention
The present invention relates to a substrate for use to make a thin-film magnetic head slider for a hard disk drive (which will be referred to herein as a “thin-film magnetic head substrate”) and also relates to a method of manufacturing such a substrate.
2. Description of the Related Art
Thanks to recent tremendous development of information and telecommunication technologies, the amount of information that can be processed by computers has increased by leaps and bounds. In particular, audiovisual (or multimedia) information such as sounds, music and video, which used to be capable of being processed only as analog signals, now can be converted into digital signals and processed by personal computers. Multimedia data such as music and video contains a huge amount of information. Thus, it has become more and more necessary to further increase the capacity of storage media for use in personal computers, for example.
A hard disk drive is a typical information storage device that has been used broadly in personal computers, for example. To meet the demand described above, the capacity of hard disks needs to be further increased and the overall size of the drive needs to be reduced. Meanwhile, a hard disk recorder for writing video data on a hard disk directly and an audio player for writing musical data on a hard disk have become increasingly popular these days. In these recorders and players, the storage capacity also needs to be further increased and the overall size of the hard disk drive also needs to be decreased to make the recorder or player ready to carry about.
FIG. 7A is a cross-sectional view schematically illustrating a thin-film magnetic head slider and surrounding portions thereof in a conventional hard disk drive. As shown in FIG. 7A, an undercoat film 13 is provided on a side surface of a base 12, which is supported on a gimbal 10. A read head 16 is provided on the undercoat film 13 and a write head 14 is further provided adjacent to the read head 16. Such a unit, including the base 12, write head 14 and read head 16 to be supported on the gimbal 10, is normally called a “head slider” or simply “slider”.
The write head 14 is made of a magnetic material and has a ring configuration, inside of which a coil 15 is wound. When a write signal is supplied to the coil 15, a magnetic field is generated in the write head 14, thereby writing data on a magnetic storage medium 17.
On the other hand, the read head 16 is a magneto-resistive (MR) or giant MR (GMR) element to convert a variation in magnetic field into a variation in electrical resistance. That is to say, the read head 16 senses a variation in the magnetic field recorded on the magnetic storage medium 17, thereby producing an electric signal representing the data that is stored on the magnetic storage medium 17.
The base 12 to hold the read head 16 and the write head 14 thereon has often been made of an Al2O3—TiC based ceramic sintered body. The Al2O3—TiC based ceramic material (which will be referred to herein as an “AlTiC material”) has been used extensively because this material exhibits excellent thermal and mechanical properties and processability while striking an adequate balance between them. However, the AlTiC material is a good electrical conductor. Accordingly, if the write head 14 were disposed adjacent to such a conductor base 12, then the write head 14 would be short-circuited and could not operate properly. Also, the surface of such an AlTiC base has pores and is not sufficiently smooth. For that reason, to electrically insulate the write head 14 from the base 12 sufficiently and increase the smoothness of the surface of the base 12, the undercoat film 13 of Al2O3 is normally provided on the side surface of the base 12. This is because Al2O3 exhibits a good electrical insulation property and has a smooth enough surface.
The conventional slider, however, has various problems to overcome.
Firstly, as it has become more and more necessary to reduce the overall size of hard disk drives, sliders also must be further reduced in size. To reduce the size of sliders, the cross-sectional area of the coil 15 inside of the write head 14 should be reduced as shown in FIG. 7B. More specifically, the inside diameter of the coil 15 needs to be minimized and yet respective loops of the coil 15 should not overlap with each other. However, when a current flows through the coil 15 with such a reduced cross-sectional area by way of terminals 18, the quantity of heat generated per unit area increases.
However, Al2O3, which has often been used as a material for the undercoat film 13, does not have such good thermal conductivity. Accordingly, the heat, generated by supplying the coil 15 with current, is shut off by the Al2O3 undercoat film 13, and cannot diffuse toward the base 12 sufficiently. Thus, the heat is stored in the read head 16 or the write head 14. As a result, the read head 16 or the write head 14 thermally expands and protrudes toward the magnetic storage medium 17 as indicated by the arrow in FIG. 7A. The gap between the read head 16 or the write head 14 and the magnetic storage medium 17 is as small as about 10 nm. Thus, it is quite possible for the thermally expanded read head 16 or write head 14 to contact with the magnetic storage medium 17 accidentally.
This phenomenon is called a “thermal pole tip recession (TPTR)”. When this phenomenon happens, the read head 16 or the write head 14 physically contacts with the magnetic storage medium, thereby scratching the magnetic storage medium or damaging the read head 16 or the write head 14 itself. Then, a serious failure might be caused, or the hard disk drive could not operate properly anymore.
Also, even if the read head 16 or the write head 14 can avoid contact with the magnetic storage medium 17, the gap between the read head 16 or the write head 14 and the magnetic storage medium 17 changes due to the thermal expansion of the read head 16 or the write head 14. For example, when the read head 16 or the write head 14 expands several nanometers, the gap between the magnetic storage medium 17 and the read head 16 or the write head 14 decreases 10% or more. Then, the read or write performance is affected significantly, and errors may be created in the signals to be written on, or read out from, the magnetic storage medium.
To overcome this problem, the undercoat film 13 may have a reduced thickness so that the heat can be dissipated into the base 12 more easily. In that case, however, static electricity might cause electrostatic breakdown or decrease the dielectric breakdown strength.
More specifically, static electricity is generated particularly easily in a hard disk drive because the rigid magnetic storage medium rotates at a high velocity. Accordingly, the static electricity is likely stored in the read head 16 and write head 14, which are provided on the undercoat film 13 made of Al2O3 with high electrical insulation property. In this case, if the undercoat film 13 is thin, then the static electricity stored is likely discharged into the base 12 that is adjacent to the undercoat film 13. As a result, dielectric breakdown occurs in the undercoat film 13 and the read and write heads 16 and 14 are damaged. Also, such a thin undercoat film 13 would have decreased electrical insulation property and allow an increased amount of leakage current to flow even if the undercoat film 13 caused no dielectric breakdown. Then, the read and write heads 16 and 14 do not operate properly any longer.
To overcome these problems, Japanese Laid-Open Publication No. 11-283221 discloses that a conventional undercoat film 13 is provided on a base 12 and an amorphous alumina film is deposited to a thickness of 100 nm to 55,000 nm on the undercoat film 13 by an ECR sputtering process. Japanese Laid-Open Publication No. 11-283221 insists that high dielectric breakdown strength is achieved by such a structure because the amorphous alumina film deposited by the ECR sputtering process has high density.
However, to obtain such a structure, an ECR sputtering system needs to be used. That is to say, two different types of systems need to be used to make the conventional undercoat film 13 and that amorphous alumina film, respectively, thus increasing the manufacturing cost of the substrate significantly.